-- Postfix `.field` / `.N` access works on any parenthesised expression,
-- not just bare identifiers. `(at rows i).2` reads column 2 of row i
-- without binding the row to a name first.
--
-- Before the fix that landed this example, the parser accepted the
-- chain only after a bare ident (`row.2`), so the agent had to spend
-- two extra tokens binding the head: `row=at rows i;row.2`. Inside
-- a HOF lambda the shape failed outright with ILO-P003 expected
-- RParen, got Dot — the parser had already returned from `(expr)`
-- when the trailing `.2` arrived.
--
-- The shape that matters most is reading one column out of each row
-- of a matrix indexed by a sparse index list — the gis-analyst
-- rerun9 originating shape (haversine row indexing).
-- (slc r 0 2).1 — numeric dot-index on a parenthesised call inside
-- an inline lambda body. The originating shape was `(at rows i).2`
-- with `rows` captured from the enclosing scope, but inline-lambda
-- capture is still tree-only on the VM/Cranelift backends today —
-- so this example uses the no-capture variant (`r` is the lambda
-- param, the parenthesised call references only it) which exercises
-- the same parser path across every engine the example harness runs.
pick-col-1 rows:L L n>L n
map (r:L n>n;(slc r 0 3).1) rows
-- (p with x:30).x — field access on a parenthesised record-update.
-- Demonstrates the same chain on a non-call grouped expression.
type point{x:n;y:n}
bumped-x>n
p=point x:10 y:20
(p with x:30).x
-- (at rs 0).?2 — safe variant. `.?N` reads as nil if out of range
-- rather than raising; same postfix chain through the helper.
safe-third rs:L L n>O n
(at rs 0).?2
-- run: pick-col-1 [[1,2,3],[4,5,6],[7,8,9]]
-- out: [2, 5, 8]
-- run: bumped-x
-- out: 30
-- run: safe-third [[10,20,30]]
-- out: 30